Cytosolic receptors of steroid hormones are homodimers in

Proteins can associate to form protein complexes , these often contain a set of proteins with similar functions, such as enzymes that carry out several steps in the same metabolic pathway. [39] This organization can allow substrate channeling , which is when the product of one enzyme is passed directly to the next enzyme in a pathway without being released into solution. [40] Channeling can make a pathway more rapid and efficient than it would be if the enzymes were randomly distributed in the cytosol, and can also prevent the release of unstable reaction intermediates. [41] Although a wide variety of metabolic pathways involve enzymes that are tightly bound to each other, others may involve more loosely associated complexes that are very difficult to study outside the cell. [42] [43] Consequently, the importance of these complexes for metabolism in general remains unclear.

Membrane abscission during cytokinesis is the process by which the membrane connecting two daughter cells is cleaved during cell division . Since it is conserved in a number of Archaea , membrane abscission is considered to be the earliest role for ESCRT machinery. [5] The process begins when the centrosomal protein CEP55 is recruited to the midbody of dividing cells in association with MKLP1, a mitotic kinesin -like protein that associates with microtubules. [5] [22] CEP55 then recruits the Vps23 subunit of ESCRT-I and accessory protein ALIX, which form into rings on either side of the midbody. [5] [10] [11] ESCRT-I and ALIX recruit ESCRT-III via its Snf7 subunit. [5] ESCRT-III subunits Vps20, Snf7, Vps24, Vps2, and Did2 form into a spiral-shaped fibril adjacent to the rings formed by Vps23. [1] [11] [18] The formation of this spiral-like structure deforms the membrane and the AAA-ATPase spastin is brought in by Did2 and Ist1 to cleave the microtubules formed at the midbody. [11] [18] Vps4 then catalyzes the disassembly of the ESCRT-III complex resulting in two newly separated daughter cells. [18] The process of membrane abscission was described using metazoan proteins as the process has been studied to a greater extent in metazoans.